It is well established that improvements in feed utilization efficiency in ruminant animals can be achieved by altering the fermentation process which takes place in the rumen. Ruminant animals utilize their food by degrading the carbohydrates contained therein to pyruvate and metabolizing the pyruvate to volatile fatty acids (VFAs) such as acetate, propionate and butyrate. These VFAs are absorbed from the gut and are employed for energy production which can then be channeled into growth, lactation, etc., by the ruminant.
The process of formation of acetate in the rumen is one of the major inefficiencies in the digestive process. Since acetate is made by the degradation of a pyruvate molecule, each molecule of acetate which is produced is accompanied by a one carbon molecule which subsequently results in the formation of methane. Most of the methane produced is lost through eructation. Since butyrate is made from two molecules of acetate, each molecule of butyrate involves the loss to the animal of two molecules of methane, with all of the associated energy.
Thus, the efficiency of carbohydrate utilization (carbohydrates being the major nutritive portion of ruminant animals' feed) can be increased by treatments which encourage the animal to produce propionate rather than acetate or butyrate from carbohydrates. Further, the efficiency of feed use can be effectively monitored by observing the production and concentration of propionate in the rumen. If the animal is making more propionate, it will be found to be using its feed more efficiently. A reduction in the amount of methane produced has also been observed to be a good indication of increased feed efficiency.
In this regard, compounds which increase the amount of propionate produced by a ruminant animal enhance the efficiency of feed utilization and have been observed to provide many beneficial results. For instance, it has been disclosed that administration of certain antibiotics which promote production of propionate can be used to promote growth rates of ruminant animals (see, e.g., Celmer et al., U.S. Pat. No. 4,431,801; Maehr, U.S. Pat. No. 4,218,560). Additionally, propionate-increasing substances have also been helpful in improving milk production in lactating ruminants (e.g., Scheifinger, U.S. Pat. Nos. 4,430,328 and 4,336,250). It is thus highly desirable to develop compounds which can increase the production of propionate in ruminant animals such as cattle, sheep or goats in order to improve feed utilization by animals which will promote the growth of the animals and also achieve improved lactation as well.